Cartridge shells and method for manufacture



Aug. 29, 1961 BLAIR, JR, ET AL 2,997,954

CARTRIDGE SHELLS AND METHOD FOR MANUFACTURE Filed Jan. 51, 1957 FIG. 1

FIG. 2

FIG. 5

JOHN R. RYAN INVENTORS AGENT.

FIG.4

United States flte'titofilice 2,997,954 CARTRIDGE SHELLS AND METHOD FOR MANUFACTURE David R. Blair, Jr., and John R. Ryan, Wilmington, Del., assignors to Hercules Powder Company, Wilmington, DeL, a corporation of Delaware Filed Jan. 31, '1957, Ser. No. 637,539 7 Claims. (Cl. 102-24) This invention relates to improved cartridge shells and to a method for their manufacture. In another aspect this invention relates to convolute paper shells which are unyielding to expansion during tamp packing of same with explosives but which, when packed with explosives, yield satisfactorily to tamping in a borehole so as to expand in diameter and fill the borehole.

A number of types of paper shells for explosive cartridges have been employed, of which convolute shells have been utilized in various forms. Various types of machines have been employed in carrying out manufacture, a common form of which has involved structure whereby a roll of paper is cut into sheets, each sheet is rolled on a mandrel to form a convolute cylinder, one end of the cylinder is crimped closed while the cylinder is on the mandrel, and the cylinder or shell is then air blown from the mandrel.

Heretofore in the manufacture of convolute paper shells to be charged with explosives there has been no gluing procedure involved, the closed end of the shell affording, in the main, the support for holding the shell intact during packing.

' Various assemblies and methods for packing such elongated paper shells with explosives have been employed exemplary of which is the well known Hall type packer which provides for tamping the explosive into the shell to a predetermined density.

A serious difficulty in the tamp packing of the unglued convolute paper shells has been in the yielding of the shell to expansion as a result of the tamp force in the shell which causes some unwrapping of the convolute roll to take place. As a result of such expansion variable loading takes place to give rather consistently a low cartridge count. Strengthening the shell by gluing or sealing the same along the entire shell length as for example along the outer edge of the topmost paper layer to secure the end of the roll to the convolute tube overcomes the difficulty of expansion of the shell during tamp packing. However, this procedure has been unsatisfactory inasmuch as the strength imparted to the shell has also precluded its expansion when tamped in the borehole, without applying an unduly excessive amount of tamp force. Sealing or gluing the paper layers as to form a laminate also imparts strength to the shell with the same result in respect to tamping in the borehole.

This invention is concerned with convolute paper shells which are glued in a novel manner so as to be unyielding to expansion during tamp packing but so as to yield to force from ordinary tamping in a borehole to expand the diameter and fill the borehole.

An object of this invention is to provide improved convolute paper shells for explosive cartridges. Another object is to provide for the manufacture of such improved convolute shells. Another object is to provide convolute paper shells for cartridges which resist expansion during tamp packing but which yield to tamp force in a borehole to expand therein. Another object is to provide a method for spot gluing a convolute paper shell for explosives to impart sufiicient strength to the shell so that it will not expand during tamp packing but will yield to expansion in the borehole as result of force of ordinary camping therein. Other aspects and objects will be ap parent from the accompanying disclosure and the appended claims.

In accordance with this invention a paper shell for an explosive cartridge is provided which comprises a convolute cylindrical paper shell closed at one end and open. at the other end; and the outside paper layer of said shell being sealed to a subjacent paper layer in a localized area closer to said open end than to said closed end. Further in accordance with this invention a method is provided which comprises rolling a paper sheet upon itself to form a convolute tube; closing one end of the said tube and maintaining the other end open; and spot sealing an outside paper layer of said tube to a layer subjacent thereto at a point closer to said open end than to said closed end.

The localized area of the seal above referred to is preferably applied subjacent to the outside end portion of the paper sheet, i.e. the top paper layer, near the open end of the shell. The said area is often no greater than about /1 of a square inch but, in any event, generally has a maximum linear dimension in any given direction, not greater than about A; to /2 the circumference of the shell. A larger area is of no particular added benefit so: far as any further contribution to stability of the shell during tamp packing is concerned, and imparts added strength to the shell to contribute to an unduly high resistance of the shell to tamping in the borehole.

Although only one spot seal is required in the practice of this invention a plurality of spot seals can be present particularly ifthey extend in a direction around the open end of the shell rather than in a longitudinal direction. To the extent that a plurality of such spots is employed and they extend longitudinally along the shell wall, they impart added strength to the shell, which is of no additional benefit to shell stability during tamp packing and which contributes to unduly high shell resistance to tamping in the borehole. The length of the shell is important in respect to disposing a plurality of spots longitudinally along the shell inasmuch as the longer the shell the greater can be the distance between spots and therefore the less eflective the spots will be in respect to unduly strengthening the tube in the borehole. We have found, however, that a single spot seal is as beneficial as a stabilizer for the shell during tamp packing as a plurality and of course imparts only a minimum strengthening effect to the shell to cause it to resist expansion from tamping force in the borehole. We therefore prefer to utilize only one spot seal which of course also simplifies manufacture and utilizes only a minimum of seal mate rial.

Any suitable glue or adhesive may be employed in the practice of this invention. When utilizing a prewaxed paper and employing a water-soluble glue, a suitable Wax solvent, e.g. carbon tetrachloride, is also applied, preferably in admixture with the glue, to cut the wax and provide a paper surface that will be operative with the glue. Whenemploying an injection nozzle or spray system, as hereinafter described, a quick drying pressure-sensitive type glue of suitable tack is advantageously employed. Shear strength is an important consideration in the selection of any glue or adhesive inasmuch as it is desired that the shear strength he sufliciently high to maintain the glue or adhesive-paper bond during the tamp packing.

By Way of further illustration, a series of paper sheets were convoluted to form shells of about 1% x 8 inches. The shells were crimped closed at one end. In each shell glue was applied as a strip under the end of the outside paper layer along its entire length, and the seal of the outside layer to the subjacent layer was completed. The

shells were tamp packed on a Hall packer and were un yielding to expansion during the entire tamp packing. However, the resulting cartridges when tested for yield ability to expansion as a result of tamping in the bore 2,997,954. l 'atente'cl Aug. 29, 1961" l- M A I.

hole, required excessive tamp rod force for expanding the cartridges to fill the borehole, which force was over 30 foot pounds. Perforations were disposed spirally along an intermediate wall of each shell as discussed, herein after to facilitate rupture of the shells in the borehole.

Another series of cartridges, the same as those above tested, were spot glued along the same path as that of the glued strips in the above tested shells. These cartridges were tamp packed under the same conditions as employed in the above-described tests. Also another series of cartridges the same except that they were unglued, were subjected to the same tamping procedure. As a result of these tests the cartridge count for the unglued cartridges was found to be in the order 131, 132, 132, 130, 130, 130 and 129, whereas for the spot glued shells the count was increased to 135, 136, 137, 137, 135, 135, 135 and 136, the cartridge count for the spot glued shells having run about /2 sticks higher than that of the unglued shells. Diameter measurements were made on a nugnber of each group of the packed cartridge as shown be ow:

Diameter at midpoint of cartridge Glued shells Unglued shells Average 1.256 Average 1.280

As shown, the spot glued shells showed practically no expansion, consonant with the appreciable increase in cartridge count.

Bursting tests, i.e. tests for resistance to expansion in the borehole in response toforce from the tamp rod, were made, the unglued shells requiring an average of about 15 foot pounds of force while the spot glued cartridges required about 17 /2 foot pounds, good expansion having been obtained in each test. A 17% foot pound value is entirely within that normally applied through the temp rod, the normal value generally running up to at least as high as 20 foot pounds and in some instances as high as 25 foot pounds. Generally, however, a value of 20 foot pounds or less is preferred.

Any suitable paper Weight can be employed depending upon the need at hand. However, a paper weight in therange of from 40 to about 95 pounds per ream is gen erally preferred. Conventional prewaxed papers, or ordinary manilla-type papers are generally utilized. The

number of wraps of paper per shell depends to a certain extent on the weight of paper employed although it is generally in the range of about 2.2-3 and very seldom greater than about 3.7 these higher numbers being cha.racteristic of use of light weights of paper. Any suitable shell sizecan be employed. Exemplary are those having a diameter of say from 78" to 2" and a length in the order of from 4" to 24" or higher. We have found that regardless of the length of the cartridge only a single spot seal need be employed.

' Any suitable method may be employed for spotting the glue or adhesive on the shell. Thus, a spraygun;

' along the longitudinal axis of the shell.

t 4 assembly illustrated hereinafter is advantageously employed. Alternatively, however, any suitable applicator system can be applied as, for example, a applicator mounted so as to support a rubber unit adapted to be dipped into a mass of glue and then contacted with the cut sheet during assembly of the latter.

As disclosed and claimed in U.S. Patent 2,378,223 assigned to Hercules Powder Company and issued June 12', 1945, paper explosive cartridges can be equipped with perforations in the side wall of the shell to weaken the wall to facilitate expansion of the same when tamped in a bore hole. The perforations are disposed on an intermediate paper layer and preferably follow a spiral path 7 Thus, the car: tridge can be formed from trapezoidal or rhomboidal sheet sections or from various polygonical shaped sheets which have a line of weakness so disposed in the surface that it will form a helical; line when the sheet is formed into "the cylinder. By way of further example is such; an explosive cartridge formed by wrapping a rhomboidal sheet of paper on itself 2% times, thereby forming a cartridge having /3 of its circumference made up of twov layers of paper and of its circumference made up of three layers of paper. The formed cartridge has located centrally of and in the middle layer of the paper forming said of its circumference comprising three layers of paper, a line of weakness consisting of perforations or slits.

Perforations employed as above. discussed, are advantageously used in conjunction with the spot seal inthe practice of this invention their function being in no way interrupted by the seal. On the other hand, if a strip of adhesive is extended along the length of the cartridge i such as subjacent the end portion of the top layer the perforations would function only after the paper had been torn away from the said seal.

By way of further illustration of the invention reference is made to the attached drawings of which FIG. 1

- shows a convolute shell with a spot of glue having been applied, and ready for rolling into form to be crimped at one end; FIG. 2 illustrates a completed shell, a portion of which is torn away to show the layer portions containing the glue spot at a point near the open end;

' FIG. 3 shows one embodiment by which a cartridge shell of this invention can be manufactured embodying the steps of rolling a cut paper sheet on a mandrel and spot gluing the underside of the paper during rolling; and. FIGURE 4 shows a completed explosive cartridge formed.

spot 11 is located in close proximity to the trailing edge.

9 at a point closer to open end 12 than to the opposite end (to be closed) 13. Generally, spot 11 is located within a distance of about the length of the axis of the shell 10, from the open end 12 in order to impart" the necessary strength to the cartridge'while it is undergoing tamp packing. End 13' when in cn'mped form (crlmp 13a) lends support to the convolute tube suflicient that spot gluing in that area of the tube is not required for stabilizing the tube during tamp packing.

With reference to FIG. 2 finished shell 10b is shown with a part of trailing portion 10a torn away to again show location of the glue spot 11 to illustrate its func' tion which is to support the outermost paper layer to the convolute tube by adhesion. Due to the shear strength of the adhesive the seal precludes the paper layers from any tendency to unwrap and consequently there is substantially no expansion during tamp' packing. The glue bond, however, is generally sufficiently weak that it is broken when subjected to force by way of the temp rod;

during tamping in the borehole. It is not necessary in all instances that the bond of glue with paper be broken particularly with reference to the longer cartridge shells, inasmuch as there still remains a relatively large portion of the shell that can be expanded as result of tearing of the paper or particularly in conjunction with perforations 20 in an intermediate paper layer as described above.

With reference to FIG. 3 is shown one method by which a paper shell of this invention can be manufactured on a mandrel with an associated nozzle or spray gun assembly for injecting the glue spot on the paper. As shown, mandrel 14 is rotated clockwise inside shield 16. Cut sheet is a paper blank preferably a rhomboidal paper section having a length and breadth of coordinating dimensions such that the proper dynamite cartridge is produced when the shell is wrapped so that all of the circumference contains at least two layers of sheet material and so that by virtue of the trailing section 10a and the corresponding leading section (not shown) the circumference contains three layers of sheet material. When desired, sheet 10 is perforated as above described so as to provide a weakened paper layer structure in the intermediate paper layer.

With reference to FIGURE 4, explosive cartridge 21 is formed from shell '10b of FIGURE 2 and contains explosive material 22, and is closed at both ends in any suitable manner preferably by crimp closures 13a and 13b. Other elements of FIGURE 4 are the same as those of FIGURES 1 and 2 and are, therefore, identified by like numerals.

Ejection nozzle 19 is disposed below laterally extending trailing portion 10a of sheet 10 and is actuated by any suitable means to eject a spray of quick-drying, pressure-sensitive type high shear strength glue, or adhesive, of good tack, on to the bottom side of trailing section 10a to form spot 11 of FIG. 1. One such means for actuating nozzle 19 includes a cam operatively connected with the mandrel which in turn operates a microswitch, the latter controlling an electrically operated air switch which controls the nozzle operation. The nozzle in a preferred form is a spray gun type of structure. Although the spot of glue can be applied to the top side of sheet 10 it is preferred to operate as shown inasmuch as the latter embodiment precludes contact of the glue with rolls 18 and shield '16 and other associated equipment.

The open end of the charged shell is closed, generally by crimping means operatively associated with the packing machine to provide an explosive cartridge of this invention.

.T he type of explosive packed in the cartridge does not alfect the function of the spot seal and it will be understood that cartridges in accordance with this invention may contain explosives which are straight dynamites, extra dynamites, gelatins, extra gelatins, semigelatins, safety explosives and the like.

The spot seal, although preferably spaced near the open end of the shell, is generally spaced a suflicient space therefrom so as to be free from contact with the shell closing operation subsequent to packing particularly when the shell is to be closed by crimping. However, we have found that certain adhesives particularly pressure-sensitive adhesives, are sufficiently flexible that they do not interfere in any way with the crimp that is formed or with the crimping operation. Further, depending on the closing procedure employed, the spot seal can be as near the open end as desired without in any way interfering with the closing of the shell or with the closure per se, such as when the closure is formed by insertion of paper cups in the shell end, or otherwise capping the shell.

The cartridge shells of this invention are not only unyielding to expansion during tamp packing but as will be readily appreciated, are unyielding to expansion during any type of packing operation as for example during packing by feeding the explosive material to the shell while maintaining the shell in a state of vibration to consolidate the charged explosive material; the spot seal maintaining the stability of the shell during vibration to preclude its expansion and to maintain substantially con stant cartridge count.

As will be evident to those skilled in the art, various modifications can be made or followed, in the light of the foregoing disclosure and discussion, without departing from the spirit or scope of the disclosure or from the scope of the claims.

What we claim and desire to protect by Letters Patent is:

1. \As an explosive cartridge, a cylindrical shell crimp closed at each end and formed from a rhornboidal paper sheet wrapped from 2.2 to 3.7 times upon itself so as to extend the resulting trailing edge along a helical path from the extremity of said shell at one end to the extremity thereof at the other end; a single spot of adhesive material intermediate, and in adhered contact with, the outermost paper layer of said shell and the paper layer of said shell immediately subjacent thereto; said spot being characterized by a linear dimension in any given direction not exceeding about one half the circumference of said shell and being closer to the end of said shell containing the least advanced portion of said trailing edge than to the opposite end of said shell; and an explosive material contained Within said shell.

2. In a cartridge of claim 1, said shell being formed from 2.2 to 3 wraps of said paper.

3. In a cartridge of claim 1 a row of perforations in an intermediate paper layer of said shell.

4. A cart-ridge of claim 1 wherein the said shot seal covers an area not exceeding about square inch.

5. An explosive cartridge of claim 1 wherein said explosive material has been tamp packed in said shell.

6. An explosive cartridge of claim 1 wherein the weight of said paper is from about 40 to about pounds per ream.

7. In the cartridge of claim 1, the said spot being located within a distance of about /3 the length of the longitudinal axis of said cylindrical shell from the said end containing the said least advanced trailing edge portion, and in close proximity to said trailing edge.

References Cited in the file of this patent UNITED STATES PATENTS 1,220,208 Ellis Mar. 27, 1917 1,450,666 Decker Apr. 3, 1923 1,831,537 McCune Nov. 10, 1931 2,062,278 Vogt Nov. 24, 1936 2,122,480 Lowey July 5, 1938 2,266,547 Goodwin Dec. 16, 1941 2,312,744 Barker Mar. 2, 1943 2,345,654 Bowman Apr. 4, 1944 2,378,223 Johnson June 12, 1945 2,604,830 Heinle July 29, 1952 2,623,445 Robinson Dec. 30, 1952 

